1. Technical Field
The present invention relates to a prestressed beam structure and the construction methods thereof in which expansion joints, which have been necessary in conventional prestressed beam structures, can be removed. Elimination of expansion joints prevents structural and functional problems associated with expansion joints, allows the span of beams to be lengthened, and reduces the amount of construction material required. The invention provides a construction method for continuously connecting one or more inner span beams with two outer span beams.
The present invention also relates to a construction method in which the prestressed beams can be made into a few short beam segments when transporting and handling long prestressed beams is difficult.
According to one aspect of the invention the prestressed beams are prefabricated and installed while the slabs are made of cast-in place concrete. According to another aspect of the invention, both the beams and the slabs are prefabricated and installed. According to another aspect of the invention, the concrete is prestressed by covering the steel beams. The invention provides an economical prestressed beam structure of high quality in a short construction period while conserving materials by utilizing the material properties of concrete and steel.
2. Background Art
Typical simple beam type prestressed beams are disclosed in Korean Patent Publication No. 88-1163 (Jul. 2, 1988) and Korean Patent Laid-open No. 92-12687 (Jul. 27, 1992) entitled "PRESTRESSED COMPOSITE BEAMS AND THE MANUFACTURING METHOD THEREOF", which provide a simple type prestressed beam, in which the cambered I-beam is first prestressed by preloading, concrete is cast on the lower flange of said prestressed I-beam, and then the preloads are removed after the concrete has cured (FIG. 4). The conventional prestressed beam of the above type is advantageous with respect to rapid construction, reduced beam depth, material conservation and improved fatigue failure strength. But, if the building is long these simple type prestressed beams must be joined to span long distances. In general, the beams in the span are connected with expansion joints.
In the case of prestressed beam bridges, the necessary expansion joints are expensive, impact driving comfort, and require maintenance. In addition, the impact of vehicles driving on the expansion joint and subsequent leakage of water on the expansion joints increases the deterioration of the bridges. The conventional prestressed beam bridges have had to use the expansion joints in spite of the above problems, because the solution to the negative moments acting on the inner supports caused by dead and live loads could not be found. In the case of prestressed beam buildings, expansion joints weaken resistance to earthquakes.
In the continuous beam structure of the present invention, however, contrary to the conventional prestressed beam structure in which expansion joints are provided in the beam joint portions, tensile stress will occur on the upper flange of the inner supports due to the negative moments caused by dead and live loads. The introduction of prestressed compressive stress against corresponding tensile stress is not considered in the conventional prestressed beam method (refer to FIG. 11).